Reference to elmer on GitHub repo page

[mark-andrews]

This issue is not about the source code in repo per se, but about the GitHub's repo webpages. Apologies if I should not be opening an issue for something not related to the source code.

As I understand it, the correct name for the package is now "ellmer" not "elmer", see #237

In that case, the link to the package website on the GitHub repo's homepage needs to be updated. Here it is as right now:

[hadley]

Thanks! Fixed now.